Q: Can I fit any Takumar M42 screw mount lens to any Asahi Pentax screw mount camera?
A: Speaking about original Asahi Pentax screw mount cameras and lenses the general answer is yes, with only one official exception, and some operation limitations. The exception is the early version of the Super-Takumar 50mm f/1.4 (eight-element construction), which cannot be screwed on Asahi Pentax screw mount bodies older than the Spotmatic (except with SV/H3v and S1a/H1a with orange R lettering on rewind knob). This is because the flipping up mirror can interfere with the protruding rear element of that lens. The second version of that same lens (seven-element construction) was redesigned and can be mounted on all bodies. Some operation limitations can also be found when coupling bodies and lenses of different age. The older one (being it the body or the lens) usually sets the performance of the combo, e.g. a full-aperture metering body (like the SPF) works in stopped-down mode with older lenses (like Super-Takumars) and a stop-down metering camera (like the SP) works in stop-down even with full-aperture lenses (like SMC Takumars). You can have full-aperture reading only by coupling cameras and lenses being both provided with proper devices. The same applies with automatic diaphragm and othere features. An interesting exception to this rule is the aperture-priority automatic exposure. To achieve it, you just need an auto-exposure body (e.g. ES, ESII) and it works with all lenses, also with older ones.Some operation problems can show up with Auto-Takumar 55m f/1.8 lenses (a forerunner of Super-Takumar lenses). Such topic is discussed here.
Q: Can I fit any M42 screw mount lens to any M42 screw mount camera?
A: The general answer is still yes, but there are exceptions. I cannot guarantee for the hundreds (probably thousands) of different M42 lenses made over the years by manufacturers worldwide. In order to prevent you won't be able to unscrew the lens, you have to check carefully that there are no risks of badly matching pins and slots or screwheads.
Such kind of problem can show up by combining SMC Takumar lenses and camera bodies other than Asahi Pentax, in case the lens mount is secured to the body by screws visible from the outside . The small sensor pin on the lens can drop into screw heads on the camera flange. At that point, detaching lens and body is an expensive repairer job, since he won't be able to dismantle the body or the lens in the ways intended by their designers. As pointed out by Mr.John Dallman, this trouble happens with Zenit B and Zenit E cameras, but I'm afraid it can happen with other camera makes too. A few Asahi Pentax models also have such screw heads on camera mount, but of course Asahi designers took care their lenses could match their bodies.
Also, you have to look for excessive protrusion of the rear glass element (or barrel), especially in case of lenses made for older cameras, usually equipped with smaller mirrors.
Q: Mercury batteries for older cameras, including most Spotmatic series, are now discontinued. Am I forced using them without their built-in TTLTTL
acronym of "Through The Lens" meter?
A: No, there are many possible solutions for powering their meter circuits. You can adapt smaller zinc-air cells (1.35V) or silver oxide batteries (1.5V). You can also buy zinc-air replacement batteries, matching both mechanical and electrical specifications for your camera. This topic is discussed in deep in a dedicated section of this website.
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